Multiple ballistic impacts of UHMWPE fiber metal laminates: Experiments and simulations

Fiber metal laminate (FML) has demonstrated great potential as a multifunctional structure with ballistic resistance capabilities. Typical projectile weapons, such as sub-machine guns or machine guns equipped with 7.62 mm ammunition, can cause multiple impacts at various locations. However, the specific behavior of FML under multiple ballistic impacts has remained unclear. To address this gap, a comprehensive investigation was conducted to explore the ballistic performance of FML under multiple impacts by a combined experimental and numerical method. The FML composed of two steel layers and one UHMWPE composite layer was subjected to both single and double impact tests. Cylindrical blunt projectiles with a caliber of 7.62 mm were utilized, with impact velocities ranging from 200 to 400 m/s. By adjusting the position of clamping fixture and keeping the projectile trajectory constant, a horizontal offset of 15 mm was set between the locations of the first and second impacts. Additionally, three-dimensional finite element simulations were employed to elucidate the penetration mechanisms of FML. The results revealed that the damage and failure caused by the first impact had minimal influence on the subsequent ballistic performance, and a consistent resistance against penetration under multiple ballistic impacts could be maintained when the spacing distance between impact points was greater than 15 mm. However, when the spacing distance was reduced, the residual velocities of FML under the three impacts gradually increased. As the velocity of the first impact was gradually increased while keeping the velocity of the second impact constant and above the ballistic limit, tearing cracks were observed to occur on the rear steel sheet of FML plate and then propagated between the penetrated holes, leading to a larger-scale failure area. Moreover, for interval time between impacts greater than 100 μs, there was no significant effect on the residual velocity of the projectiles.